Fabrication Of Patterned And Highly Sensitive Mechanochromic Photonic Hydrogels

Photonic crystals?PCs? are materials patterned with a periodicity.Responsive photonic crystals?RPCs?have photonic bandgap responding to external environments.There are numerous preparation methods of RPCs,among which photonic crystals by using colloidal crystals as templates have apparent advantages and have become one of the research hotspots for photonic crystal materials.Magnetic nanoparticles?NPs?can self-assemble into uniform 1D nano-chain structure rapidly under magnetic field,which can be used as building blocks to shorten the preparation time of RPCs.Though frequently reported in recent years,mechanochromic PCs still have several disadvantages,mechanical instability,un-adjustable excitability.Here,we use a simple method to prepare mechanochromic PCs,whose mechanical excitability can be adjusted effectively.On the other hand,existing problems in current patterned RPCs are complex preparation processes,bad monochromaticity,and hardly controlled full color display.Thus,we designed full color display patterned PCs based on RPCs with thermal/light responsive and bright structure color features.In this thesis,Fe₃O₄@C NPs were used as building block for preparation of mechanochromic PCs and patterned RPCs,which are as follows:?1?Mechanochromic PCs with adjustable mechanical excitability were developed here.Fe₃O₄@C nanoparticles were synthesized through one-step solvothermal process.Such particles were used as building blocks mixing with PEG for constructing photonic hydrogel in acrylamide by UV-curing with the existence of magnetic field;then PEG molecules were removed by soaking in water.Mechanical responsiveness and mechanical excitability of the photonic hydrogels with different PEG content were investigated.The results indicated that the PEG content mixed in photonic hydrogel film has a significant influence on the mechanical excitability of photonic hydrogel film.Increasing PEG content resulted in larger reflected wavelength shift of photonic hydrogel film.Such photonic hydrogel films are sensitive to different pressure and the mechanical excitability is easily adjusted by PEG content.?2?Invisible photonic prints with differential color shifting properties by localized interpenetrating polymer networks?IPN?were developed here,which can be shown by thermal stimulation.This newly designed photonic hydrogel was prepared through two-step UV-curing.Patterned photonic crystal with localized IPN is consists of PNIPAM area and PNIPAM/PAM IPN area.By increasing temperature,the shrinking degrees of PNIPAM area and PNIPAM/PAM IPN area are different which leads to the prints showing.Moreover,the existence of PNIPAM/PAM IPN area has positive effect on the wavelength shifting degree of PNIPAM area varies from different temperature since PNIPAM area and PNIPAM/PAM IPN area are inter-connected.The as-prepared photonic hydrogel with localized IPN can realize full color pattern display under thermal/light stimulations.